Select the range of supposed email addresses and use F&R, Regular expression enabled with Current selection only.
Enter exactly ^[^@]+$
in the field behind “Find:”, the order Find All
.
(RegEx can also “search negative”. If you need to understand, study Regular Expression Tutorial - Learn How to Use Regular Expressions, The +
in place of the *
used by @JohnSUN avoids to find empty cells.)
[Edit 1]
For what you need to do, filtering might be the better means:
Select the column containing the email addresses, go >Data>More Filters>Standard Filter
The dialog that opens will offer the variant Does not contain
under Condition, and you only need to enter the @
then under Value.
[/Edit 1]